diff --git a/lib/extramath.js b/lib/extramath.js
index 0673dd8..cd33a66 100644
--- a/lib/extramath.js
+++ b/lib/extramath.js
@@ -1,5 +1,7 @@
-// lib/extramath.js
+// extramath.js
+// Namhyeon Go <abuse@catswords.net>
 // https://github.com/gnh1201/welsonjs
+// https://app.rdbl.io/T0AB411UHDW9/S0VLKP4HKVGC/P0TL9IQZOUFT
 
 // DTM(Document-term Matrix): https://en.wikipedia.org/wiki/Document-term_matrix
 function DTM() {